Some of the design issues for this network include;

· Power supplies are directly connected to the network power lines.

· Length to speed is 156m/78m/39m to 125Kbps/250Kbps/500Kbps respectively.

· A single drop is limited to 6m.

· Each node on the network will have its own address between 0 and 63.

If a PLC-5 was to be connected to Devicenet a scanner card would need to be placed in the rack. The ladder logic in See Communicating with Devicenet Inputs and Outputs would communicate with the sensors through a scanner card in slot 3. The read and write blocks would read and write the Devicenet input values to integer memory from N7:40 to N7:59. The outputs would be copied from the integer memory between N7:20 to N7:39. The ladder logic to process inputs and outputs would need to examine and set bits in integer memory.

Communicating with Devicenet Inputs and Outputs

On an Allen Bradley Softlogix PLC the I/O will be copied into blocks of integer memory. These blocks are selected by the user in setup software. The ladder logic would then using integer memory for inputs and outputs, as shown in See Devicenet Inputs and Outputs in Software Based PLCs. Here the inputs are copied into N9 integer memory, and the outputs are set by copying the N10 block of memory back to the outputs.

Devicenet Inputs and Outputs in Software Based PLCs